Process fluid or gas bearings are now being utilized in an increasing number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween filled with a fluid such as air, which, under dynamic conditions, form a supporting wedge sufficient to prevent contact between the two relatively movable elements.
Improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively movable bearing elements. Such foils, which are generally thin sheets of a compliant material, are deflected by the hydrodynamic film forces between adjacent bearing surfaces. The foils enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect.
The ready availability of relatively clean process fluid or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid film lubricated, bearings particularly attractive for high speed rotating machinery. While in many cases the hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary to externally pressurize the fluid between the bearing surfaces to increase the load carrying capability.
In order to properly position the compliant foils between the relatively movable bearing elements, a number of mounting means have been devised. In thrust bearings, it is conventional practice to mount a plurality of individually spaced foils on a foil bearing disk such as by spot welds and position the foil bearing disk on one of the bearing elements as exemplified in U.S. Pat. No. 3,635,534. Alternatively, a compliant unitary foil, such as illustrated in U.S. Pat. No. 4,247,155, has been proposed.
To establish stability of the foils in most of these mounting means, a substantial pre-load is required on the foil. That is, the individual foils must be loaded against the relatively movable bearing element opposed to the bearing element upon which the foils are mounted. It has been conventional to provide separate compliant stiffener elements or undersprings beneath the foils to supply this required preload as exemplified in Applicant and Assignee's previous U.S. Pat. Nos. 4,624,583 and 4,682,900. Further examples of current underspring designs are exemplified by U.S. Pat. Nos. 4,082,375; 4,213,657; 4,225,196; 4,247,155; 4,277,111; and 4,277,112. While these references detail underspring designs of various configurations, it is important to note that the associated thrust load capacities is limited to about 40 pounds per square inch (psi). Further, the designs attempt to provide either a radially uniform underspring force, or a radially decreasing underspring force, as discussed in the Grey, U.S. Pat. No. 4,277,111.